1. Field of the Invention
Traditional radiation reflectors usually employ reflective surfaces similar to parabolic, elliptical, cylindrical-parabolic or cylindrical-elliptical mirrors. As a result of this the radiation flux is projected with a distribution which is often highly inhomogeneous and with imprecise aperture angles, entailing significant losses of efficiency and also causing glare beyond the required apertures.
The lack of homogeneity is partially remedied by making the surface of these mirrors irregular or diffusive, which further reduces the efficiency and further randomises the aperture angles. In the case of point or quasi-point sources like xenon arc lamps and metal halogenide lamps, the lack of homogeneity becomes so serious that it is no longer possible to render it acceptable with acceptable conditions of efficiency and aperture angle control.
2. Description of Related Art
The applicant has also proposed, notably in patent Nos. FR-A-1.602.203, FR-A-2.224.769 and FR-A-2.224.770, to use optimised conoid or pyramidal mirrors which make it possible to obtain with traditional sources of radiation projected fluxes featuring good homogeneity and high efficiency within relatively precise aperture angles.
The terms conoid and pyramidal mirror designate a mirror having the shape of the lateral surface of a geometrical solid delimited by two bases, permeable to the radiation, parallel to each other and of unequal area, the cross-section parallel to the bases of this solid increasing progressively from the smaller base, which acts as the flux input section, to the larger base, which acts as the flux output section, the two bases being linked by reflective lateral surfaces, contiguous or otherwise, and the geometric solid having at least two planes of symmetry perpendicular to the bases. The intersection of these planes of symmetry constitutes the mean optical axis of the conoid or pyramidal mirror. The simplest conoid is the cone, but all manner of varieties may be employed to adapt the reflector to the geometry of the source and to that required of the beam. Specifically, the term pyramidal mirror means a mirror of this kind in which the bases are substantially polygonal and the reflective lateral surfaces, contiguous or otherwise, are plane or slightly curved or cambered.
The source of radiation and/or images of this source are disposed in the smaller section of the conoid or pyramidal mirror. An associated collector mirror is used to recover radiation emitted towards the rear of the conoid or pyramidal mirror.
When the source of radiation is a point or quasi-point source, shortcomings in respect of homogeneity can no longer be suitably reduced by these conoid or pyramidal mirrors of currently known design. Appropriate correction requires that the source of radiation and/or its images occupy a significant fraction of the small section of the conoid or pyramidal mirror, so that the flux emanating from this input section has a distribution that is as close to the Lambert distribution as possible. This is no longer the case when the source is a point or quasi-point source. It results in areas of increased and reduced brightness on the planes onto which the flux is projected, with considerable nuisance, value.